The term “overweight” refers to body weight above a normal range. Overweight and obesity are determined by calculating the body mass index (BMI), the weight in kilograms divided by height in meters squared. Overweight is generally defined as a BMI of 25 to 29.9 kg/m2, obesity is generally defined as a BMI of ≧30 kg/m2, and severe obesity is generally defined as a BMI≧40 kg/m2 (or BMI≧35 kg/m2 in the presence of other medical comorbidities). A BMI less than about 22.0 kg/m2 is ideal, though this may be a difficult and perhaps unrealistic goal for many individuals.
Overweight and obesity are worldwide health epidemics, with increasing prevalence. In the United States, more than two-thirds of Americans are overweight and 26-55% are obese based on data collected in 2007 by the Centers for Disease Control and National Institutes of Health. Globally, overweight and obesity affects both established and developing countries. For example, about 23% of the population in the United Kingdom is obese, compared to about 11-23% in Mexico, approximately 30-40% in South Africa, and about 10% in Pakistan.
Overweight and obesity are associated with Many health risks including type 2 diabetes mellitus, hypertension, dyslipidemia, coronary heart disease, cancer and stroke among others, as well as premature death. Compared to normal weight individuals, a BMI of 26.5 to 29.9 kg/m2 is associated with a 1.5 times increased risk of death. Those with a BMI≧30 kg/m2 have a 2-3 fold increased risk of all-cause mortality. The economic implications are great; a Brookings institute publication quoted the cost to the United States of overweight and obesity to be at least $147 billion annually. The rationale for weight reduction is clear, from both a medical and economic perspective.
Currently available methods to decrease weight include behavior modification (dietary change and exercise regimens), drug therapy, and bariatric surgery. Drug therapy is indicated in patients who have failed to achieve weight loss goals through diet and exercise alone. The FDA has approved two classes of medications explicitly for use in weight loss. Sympathomimetic drugs (e.g., phendimetrazine, diethylpropion, phentermine) stimulate the release of norepinephrine and/or inhibit its reuptake into nerve terminals. In lay terms, this effect is analogous though much stronger than that produced by caffeine. Sympathomimetics cause appetite suppression but also may cause hypertension and potentially myocardial infarction, and as a result are limited to <12 weeks of use by the FDA. Ephedrine is a member of this class that was recently removed from the market because of these adverse side effects.
Malabsorptive drugs are the other medication class that is FDA approved for use in obesity. Orlistat is the only representative of this group. Orlistat alters fat digestion by inhibiting pancreatic lipase, resulting in the malabsorption of 30% of ingested fat. Instead of being taken up by the body, this fat is excreted in stool. Orlistat is the only FDA approved medication for obesity that is acceptable for long term use (up to 4 years).
For patients with severe obesity, the only proven mechanism of long-term weight loss is bariatric surgery. Bariatric surgery effects weight loss through either malabsorption and/or restriction. Malabsorption (as with Orlistat above) means the incomplete absorption of ingested food. The body does not absorb the full amount of calories present in a meal or in a given food item. Restriction means a reduction in the size of the stomach, with resultant early satiety and reduced food consumption.
Overweight and obese patients who do not meet BMI criteria for severe obesity do not have surgery as an available option for weight loss, as insurance coverage for these procedures is typically limited to the severely obese. Accordingly, overweight and obese patients have access to only one FDA approved medication for weight loss. Thus, there exists a great need for weight loss and weight control alternatives.